Arsenic is one of the five most common inorganic contaminants at Superfund sites. In addition, water providers, solid waste disposal entities, and regulatory agencies are gearing up to comply with a new standard for arsenic in drinking water, by evaluating arsenic removal options and the implications of residuals disposal. Consequently, it is critical to have appropriate treatment options identified for a variety of arsenic in water conditions and appropriate methods developed for assessing the hazard posed by the arsenic-bearing residuals that inevitably must be produced. Furthermore, to the degree that arsenic-bearing residuals are shown to pose an unacceptable risk, technologies must be developed to stabilize these residuals and mitigate the risk to an acceptable level. If this latter need is left unaddressed, it is foreseeable the disposed residuals will become the focus of future Superfund clean-ups. This project focuses on addressing shortcomings and providing advances in three critical areas: treatment technologies, residuals assessment and residuals stabilization. Separate, yet interdependent research study areas are directly aligned with these critical areas. The first study area involves development and testing of two innovative approaches for removing arsenic from water. One approach aims at meeting the need for a robust, compact, economical and low maintenance technology for arsenic removal from drinking water by small utilities. The second addresses the need for a technology for selective arsenic removal from high concentration, complex aqueous matrices such as ion exchange brines and membrane process concentrates. The second research study area involves development, mechanistic interpretation and validation of a testing protocol to assess arsenic and other hazardous oxyanion leaching from solids under landfill conditions. Specific shortcomings of currently used protocols will be identified and a widely applicable, abiotic protocol will be developed and tested for the range of solid residuals that are expected to be generated by technologies for removing arsenic from water. The final research study area involves development, mechanistic interpretation and testing of two technologies to produce environmentally benign arsenic treatment residuals. An encapsulation technology is refined and tested for application on residuals of current arsenic adsorption technologies, including those with high salt contents. In a complementary effort, an innovative crystallization technology will be studied and taken to proof of concept for long-term, high stability, near-minimum volume disposal of arsenic-laden iron sludges. These sludges will be the residuals generated from the innovative removal technologies developed in this project and potentially generated in ion exchange and membrane processes.